Maria Trilogy: Episode 2 - The Secret of the Mark

This series is definitely not for everyone. It's easier to recommend this one over the Maria trilogy because instead of playing as a child abuser you're playing as a police officer to catch them. It's slightly less disturbing but still very much so. It's the same kind of which are often well done. However some are not like typical escape style puzzles and you will need some knowledge or skills (e.g. mathematical unit conversion). The hints aren't too helpful for this either, but will show you how to get the solution while also showing you the solution, instead of just giving you the information to figure it out yourself.